The following are the three main methods known for measuring the rotation speed of spherical moving bodies: (1) take video of the spherical moving body, and calculate the rotation speed using image analysis technology (for example, see Japanese Unexamined Patent Application Publication No. 2006-234485A), (2) install an acceleration sensor within the spherical body, and measure the rotation speed from the periodicity of the acceleration data obtained (for example, see Japanese Unexamined Patent Application Publication No. 2010-256068A), and (3) the Doppler method of generating a radio wave for transmission from an antenna as a transmission wave, and calculating the movement speed of the moving body from the change in the frequency of the reflection wave from the moving body (for example, see Japanese Unexamined Patent Application Publication Nos. 2003-294777A and 2003-043141A, and US Patent No. 6244971B).
However, of the conventional technologies as described above, in the method of using image analysis technology described in (1), a camera or the like is used for taking the video, so a large-scale system is necessary, which has the problem that a large cost is involved. Also, in the method of (1), it is difficult to measure the rotation speed automatically, for example there is the problem that it is difficult for a user to measure the rotation speed of their own pitching.
Also, in the method of installing an acceleration sensor within the spherical body as described in (2) above, it is difficult to make the properties and performance of the spherical body the same as a normal spherical body, so there is the problem that the field of application is limited. Also, in the Doppler method described in (3) above, normally the radio wave transmission equipment and receiving equipment are separate, which has the problem that it is difficult to carry out stable measurement. Also, in the method described in (3) above, there is the problem that it is difficult to reduce the size of the measurement equipment.